Cooling passages for a mid-turbine frame

ABSTRACT

A mid-turbine frame for a gas turbine engine includes an inner frame case. A bearing support member is located adjacent the inner frame case. At least one spoke is attached to the inner frame case. At least one spoke includes a cooling airflow passage that extends through the inner frame case and the bearing support member.

BACKGROUND

The present disclosure relates generally to a gas turbine engine, and inparticular to a mid-turbine frame (MTF) included in a gas turbineengine.

A gas turbine engine typically includes a fan section, a compressorsection, a combustor section, and a turbine section. Air entering thecompressor section is compressed and delivered into the combustionsection where it is mixed with fuel and ignited to generate a high-speedexhaust gas flow. The high-speed exhaust gas flow expands through theturbine section to drive the compressor and the fan section.

A mid-turbine frame (MTF) is positioned between a high pressure turbinestage and a low pressure turbine stage of a gas turbine engine. The MTFsupports one or more bearings and transfers bearing loads from an innerportion of the gas turbine engine to an outer engine frame. The MTF alsoserves to route air from the high pressure turbine stage to the lowpressure turbine stage.

SUMMARY

In one exemplary embodiment, a mid-turbine frame for a gas turbineengine includes an inner frame case. A bearing support member is locatedadjacent the inner frame case. At least one spoke is attached to theinner frame case. At least one spoke includes a cooling airflow passagethat extends through the inner frame case and the bearing supportmember.

In a further embodiment of the above, at least one spoke includes anelongated cylindrical portion that extends in a radial direction andforms the cooling airflow passage and has a branch that extends in anaxial direction.

In a further embodiment of any of the above, the cooling airflow passageincludes a branch that extends in a radial direction.

In a further embodiment of any of the above, the branch that extends inthe radial direction is in fluid communication with a bearing supportcavity.

In a further embodiment of any of the above, a fitting connects thecooling airflow passage to the inner frame case and the bearing supportmember. The fitting includes a transfer tube that connects at least onespoke to a cup boss. The transfer tube is fixed relative to at least onespoke and moveable relative to the cup boss.

In a further embodiment of any of the above, a swirler tube is connectedto the fitting for directing cooling airflow in a direction of rotationof a low pressure rotor.

In a further embodiment of any of the above, the cooling airflow passageincludes a circular cross section in a first portion of the cup boss anda race track cross section in a second portion of the cup boss.

In a further embodiment of any of the above, the inner frame case andthe bearing support member each include a race track shaped openingaligned with the cooling airflow passage.

In another exemplary embodiment, a gas turbine engine includes amid-turbine frame located axially between a first turbine and a secondturbine. The mid-turbine frame includes an inner frame case. A bearingsupport member is located adjacent the inner frame case. At least onespoke is attached to the inner frame case. At least one spoke includes acooling airflow passage that extends through the inner frame case andthe bearing support member.

In a further embodiment of any of the above, at least one spoke includesan elongated cylindrical portion that extends in a radial direction andforms the cooling airflow passage and has a branch that extends in anaxial direction.

In a further embodiment of any of the above, the cooling airflow passageincludes a branch that extends in a radial direction.

In a further embodiment of any of the above, the branch that extends inthe radial direction is in fluid communication with a bearing supportcavity.

In a further embodiment of any of the above, a fitting connects thecooling airflow passage to the inner frame case and the bearing supportmember. The fitting includes a transfer tube that connects at least onespoke to a cup boss. The transfer tube is fixed relative to at least onespoke and moveable relative to the cup boss.

In a further embodiment of any of the above, a swirler tube is connectedto the fitting for directing cooling airflow in a direction of rotationof a low pressure rotor.

In a further embodiment of any of the above, the cooling airflow passageincludes a circular cross section in a first portion of the cup boss anda race track cross section in a second portion of the cup boss.

In a further embodiment of any of the above, the inner frame case andthe bearing support member each include a race track shaped openingaligned with the cooling airflow passage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an example gas turbine engine.

FIG. 2 is a schematic perspective view of an example mid-turbine framein the gas turbine engine.

FIG. 3 is a cross section view taken along line 3-3 of FIG. 2.

FIG. 4 is a perspective view of an example I-rod.

FIG. 5 is another perspective view of the example I-rod.

FIG. 6 is a sectional view taken along line 5-5 of FIG. 4.

FIG. 7 is a sectional view taken along line 6-6 of FIG. 4.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flow path B in abypass duct defined within a nacelle 15, while the compressor section 24drives air along a core flow path C for compression and communicationinto the combustor section 26 then expansion through the turbine section28. Although depicted as a two-spool turbofan gas turbine engine in thedisclosed non-limiting embodiment, it should be understood that theconcepts described herein are not limited to use with two-spoolturbofans as the teachings may be applied to other types of turbineengines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a first (or low) pressure compressor 44 and afirst (or low) pressure turbine 46. The inner shaft 40 is connected tothe fan 42 through a speed change mechanism, which in exemplary gasturbine engine 20 is illustrated as a geared architecture 48 to drivethe fan 42 at a lower speed than the low speed spool 30. The high speedspool 32 includes an outer shaft 50 that interconnects a second (orhigh) pressure compressor 52 and a second (or high) pressure turbine 54.A combustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 57 of the engine static structure 36 is arranged generally betweenthe high pressure turbine 54 and the low pressure turbine 46. Themid-turbine frame 57 further supports bearing systems 38 in the turbinesection 28. The inner shaft 40 and the outer shaft 50 are concentric androtate via bearing systems 38 about the engine central longitudinal axisA which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of combustor section 26 or even aft ofturbine section 28, and fan section 22 may be positioned forward or aftof the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five 5:1. Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present invention isapplicable to other gas turbine engines including direct driveturbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft(10,668 meters), with the engine at its best fuel consumption—also knownas “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is theindustry standard parameter of lbm of fuel being burned divided by lbfof thrust the engine produces at that minimum point. “Low fan pressureratio” is the pressure ratio across the fan blade alone, without a FanExit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosedherein according to one non-limiting embodiment is less than about 1.45.“Low corrected fan tip speed” is the actual fan tip speed in ft/secdivided by an industry standard temperature correction of [(Tram °R)/(518.7° R)]^(0.5). The “Low corrected fan tip speed” as disclosedherein according to one non-limiting embodiment is less than about 1150ft/second (350.5 meters/second).

The example gas turbine engine includes fan 42 that comprises in onenon-limiting embodiment less than about 26 fan blades. In anothernon-limiting embodiment, fan section 22 includes less than about 20 fanblades. Moreover, in one disclosed embodiment low pressure turbine 46includes no more than about 6 turbine rotors schematically indicated at34. In another non-limiting example embodiment low pressure turbine 46includes about 3 turbine rotors. A ratio between number of fan blades 42and the number of low pressure turbine rotors is between about 3.3 andabout 8.6. The example low pressure turbine 46 provides the drivingpower to rotate fan section 22 and therefore the relationship betweenthe number of turbine rotors 34 in low pressure turbine 46 and number ofblades 42 in fan section 22 disclose an example gas turbine engine 20with increased power transfer efficiency.

FIG. 2 is a schematic perspective view of one embodiment of mid-turbineframe 57. The schematic view shown in FIG. 2 is high level conceptualview and is intended to illustrate relative positioning of variouscomponents, but not actual shape of various components. The mid-turbineframe 57 includes an outer frame case 62, an inner frame case 64, and aplurality of hollow spokes 65. The outer frame case 62 includes an outerdiameter surface 66. The inner frame case 64 includes an outer diametersurface 70 and an inner diameter surface 72. In the embodiment shown inFIG. 2, six hollow spokes 65 are distributed evenly around thecircumference of the inner frame case 64 to provide structural supportbetween the inner frame case 64 and the outer frame case 62. In theillustrated embodiment, each of the hollow spokes 65 is directlyopposite (i.e. 180 degrees from) another of the hollow spokes 65. Inalternative embodiments, the mid-turbine frame 57 can have an evennumber of hollow spokes greater than or less than six.

The inner frame case 64 supports the rotor assembly via the bearingsystems 38 (shown in FIG. 1), and distributes the force from the innerframe case 64 to the outer frame case 62 via the plurality of hollowspokes 65. Attachment of the hollow spokes 65 to the outer frame case 62is provided at a plurality of bosses 75 located circumferentially aroundthe outer diameter surface 66 of the outer frame case 62.

In one embodiment, attachment of the hollow spokes 65 at the pluralityof bosses 75 may be secured by a retaining nut (shown in FIG. 3) thatallows the hollow spokes 65 to be tensioned. The hollow spokes 65 can betensioned via a threaded connection so as to remain in tension duringsubstantially all operating conditions of gas turbine engine 20.Apertures 76 formed in each of the plurality of bosses 75 allow coolingairflow to be distributed into a hollow portion of each of the hollowspokes 65. In this way, the cooling airflow is directed from the outerdiameter through the hollow portions of the cooled hollow spokes 65towards the inner frame case 64. The cooling airflow can function tocool the hollow spokes 65 and also to cool components radially inward ofthe inner frame case 64, such as the bearing systems 38.

FIG. 3 is a cross-sectional view of the mid-turbine frame 57 taken alongline 3-3 of FIG. 2. A hollow spoke 65A is one example of the hollowspokes 65 shown in FIG. 2. The hollow spoke 65A extends from the outerframe case 62 through the airfoil 59 to the inner frame case 64. Theairfoil 59 extends from an outer platform 78 to an inner platform 80. Inthe illustrated embodiment, the airfoil 59, the outer platform 78, andthe inner platform 80 are integrally formed, and are all positionedradially inward of the outer frame case 62 and radially outward of theinner frame case 64. The airfoil 59, the outer platform 78, and theinner platform 80 define a portion of the core flow path C at themid-turbine frame 57. The airfoil 59 extends axially from a leading edge82 to a trailing edge 84. The airfoil 59 is oblong so as to be longer inthe axial direction than in the circumferential direction. The airfoil59 has a hollow interior 86, which is also relatively narrow in acircumferential direction.

In the illustrated embodiment, the hollow spoke 65A includes a tie rod90A and a retaining nut 92. The tie rod 90A is an elongated hollow tubethat includes a threaded surface 94 at a radially outer end and a flange96 at a radially inner end. The threaded surface 94 is on an outersurface 98 of the tie rod 90A. An inner passage surface 100 of the tierod 90A defines an inlet passage 118 through the tie rod 90A. The tierod 90A tapers along its length from the flange 96 at its radially innerend to the threaded surface 94 at its radially outer end.

The retaining nut 92 includes a threaded surface 102 at a radially innerend of the retaining nut 92 and a flange 104 at a radially outer end ofthe retaining nut 92. The threaded surface 102 is on an inner surface106 of the retaining nut 92. The flange 104 extends outward from anouter surface 108 of the retaining nut 92.

In the illustrated embodiment, the flange 96 of the tie rod 90A abutsagainst the inner frame case 64 so that the inner passage surface 100aligns with a hole 110A in the inner frame case 64. The flange 96 isattached to the inner frame case 64 via bolts 112. The retaining nut 92extends through a hole 114 in the outer frame case 62 such that theflange 104 abuts against the outer diameter surface 66 of the outerframe case 62. The flange 104 is attached to the outer frame case 62 viaa bolt 116. The bolt 116 extends through the flange 104 into the outerframe case 62. The tie rod 90A is threaded into the retaining nut 92 toattach the tie rod 90A to the retaining nut 92. In the illustratedembodiment, a portion but not all of the threaded surface 94 overlapswith a portion but not all of the threaded surface 102.

During assembly, the tie rod 90A is inserted through the hollow interior86 of the airfoil 59 in a direction from radially inward to radiallyoutward. The inner frame case 64 is then positioned radially inward ofthe tie rod 90A and attached to the tie rod 90A by the bolts 112. Theretaining nut 92 is then inserted through the hole 114 and threadedlyengaged with the tie rod 90A. The retaining nut 92 can be tightened, asdesired, in a manner described below. Once the retaining nut 92 issuitably tightened on the tie rod 90A, the bolt 116 is inserted to fixthe retaining nut 92 to the outer frame case 62 to prevent the retainingnut 92 from rotating and loosening.

Because the threaded surface 94 overlaps with the threaded surface 102only partially, the threaded connection between the retaining nut 92 andthe tie rod 90A is variable. The retaining nut 92 does not bottom out atany particular point when threaded on the tie rod 90A. This allows theretaining nut 92 to be threaded on the tie rod 90A to an extentdetermined during assembly, not predetermined prior to assembly. Thisallows the hollow spoke 65A, and the mid-turbine frame 57 in general, tobe relatively insensitive to manufacturing tolerances.

The inlet passage 118 branches off between a first branch 120 extendinginto a bearing support cavity 122 and a second branch 124 extending intoa low-rotor cavity 126. The bearing support cavity 122 is at leastpartially defined by the inner frame case 64 and a bearing supportmember 123. The first branch 120 extends in a radially inward directionthrough the inner frame case 64. The bearing support member 123 carriesstructural load from the inner frame case 64 to the bearing interfacewith the outer shaft 50. The bearing support member 123 has a boltedflange 125 for connecting to the inner frame case 64.

A plug 128 is aligned with the first branch 120 and is located in anopening 130 in the hollow spoke 65A adjacent the outer diameter surface70 of the inner frame case 64. The plug 128 includes an opening 129having a conical radially outer portion that tapers to a cylindricalchannel on a radially inner side. The cylindrical channel of the plug128 includes a diameter D1 that is smaller than a diameter D2 defined bythe inner passage surface 100.

In the illustrated example, the plug 128 includes a diameter D1,however, the diameter D1 could be any dimension that is smaller than thedimension D2 in order to control the amount of cooling airflow thattravels into the bearing support cavity 122. The cooling airflowentering the bearing support cavity 122 maintains positive pressureinside the bearing support cavity 122 in order to cool the adjacentcomponents and prevent ingestion of hotter gases from the cavity betweenthe vane platform 80 and the inner frame case 64. A piston seal 146 islocated adjacent the inner frame case 64 to minimize the leakage flowfrom the bearing support cavity 122 axially forward towards the highpressure turbine 54.

Although the plug 128 is shown contacting the hollow spoke 65 a and theinner frame case 64, the plug 128 could be located anywhere within thefirst branch 120. Alternatively, the plug 128 could be solid and preventthe cooling airflow from entering the bearing support cavity 122 so theentire cooling airflow must travel through the second branch 124.Alternatively, rather than a separate piece, the reduced diameter D1could be integral to the inner frame case 64 or the hollow spoke 65 a.

The second branch 124 extends in an axially downstream directionperpendicular to the first branch 120. Although the second branch 124 isshown being perpendicular to the first branch 120, the second branch 124could be within 20 degrees of being perpendicular to the first branch120. The second branch 124 is in fluid communication with the low rotorcavity through to a fitting 132 that extends through the inner framecase 64 and the bearing support member 123 where they are boltedtogether at the flange 125. The second branch 124 continues into the lowturbine rotor cavity 126 via a swirler tube 142.

The fitting 132 includes a transfer tube 134 pressed into an opening 138in the hollow spoke 65A on a first end and engages a cup boss 136 on asecond end. A piston seal creates a seal between an outer diameter ofthe transfer tube 134 and the cup boss 136. As shown in FIG. 4, the cupboss 136 is fastened to the inner frame case 64 with fasteners 140 andis aligned with a hole 110B in the inner frame case 64 and a hole 110Cin the bearing support member 123. The fasteners 140 also secure theswirler tube 142 to an opposite side of the bearing support member 123from the inner frame case 64. The swirler tube 142 directs the coolingairflow into the low rotor cavity in the direction of rotation of thelow rotor to reduce turning and aerodynamic losses in the coolingairflow.

A restricting ring 144 is located between the swirler tube 142 and theinner bearing support member 123. The restricting ring 144 includes anarea A3 which is smaller than the area defined by diameter D4 of thesecond branch 124. The restricting ring 144 restricts the amount ofcooling airflow through the second branch 124 to aid in dividing theamount of cooling airflow traveling into the bearing support cavity 122and the low-rotor cavity 126. Although the restricting ring 144 is shownbetween the swirler tube 142 and bearing support member 123, therestricting ring 144 could be located anywhere within the second branch124 to reduce the cooling airflow into the low-rotor cavity 126. In oneexample, a first portion of cooling airflow travels into the bearingsupport cavity 122 and a second portion of cooling airflow travels intothe low-rotor cavity 126, with the second portion being greater than thefirst portion. The restricting area A3 could alternatively be formed bythe hole through the flange 125, or be integrally formed by a feature inthe cup boss 136 or swirler tube 142.

FIGS. 4 and 5 are perspective views of the tie rod 90A. The tie rod 90Aincludes three fastener openings 150 for securing the tie rod 90A to theinner frame case 64 with the bolts 112. Bushings 152 are aligned withthe fastener openings 150 and include tabs 154 that prevent rotation ofthe bushing 152 relative to the tie rod 90A by engaging a portion of thetie rod 90A. A first buttress 97 extends between the outer surface 98 ofthe tie rod 90A and the flange 96 and includes an upper surface at anangle σ relative to the flange 96. In one example, the angle σ is 56degrees and in another example, the angle σ is between 36 and 76degrees.

The fasteners 140 engage clinch nuts 154 with anti-rotation features 156that engage the cup boss 136 to prevent the clinch nuts 154 fromrotating relative to the cup boss 136.

As shown in FIGS. 6 and 7, a shape of the second branch 124 passingthrough the cup boss 136 has a varying cross section. A portion of thesecond branch 124 in the cup boss 136 adjacent the transfer tube 134includes a circular cross section and a portion of the second branch 124in the cup boss 136 closer to the inner frame case 64 includes a racetrack shaped cross section. The race track shaped cross section includesa pair of opposing parallel sides connected by a pair of rounded ends.The holes 110B and 110C and the swirler tube 142 also have a race trackcross section that aid in diffusing the cooling airflow travelingthrough the second branch 124. Alternatively, the racetrack sectioncould be an arcuate racetrack, oval, elliptical, or simply circular incross section.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can only be determined by studying the following claims.

What is claimed is:
 1. A mid-turbine frame for a gas turbine enginecomprising: an inner frame case; a bearing support member locatedadjacent the inner frame case; and at least one spoke attached to theinner frame case, wherein the at least one spoke includes a coolingairflow passage extending through the inner frame case and the bearingsupport member.
 2. The mid-turbine frame of claim 1, wherein the atleast one spoke includes an elongated cylindrical portion extending in aradial direction forming the cooling airflow passage having a branchextending in an axial direction.
 3. The mid-turbine frame of claim 2,wherein the cooling airflow passage includes a branch extending in aradial direction.
 4. The mid-turbine frame of claim 3, wherein thebranch extending in the radial direction is in fluid communication witha bearing support cavity.
 5. The mid-turbine frame of claim 1, furthercomprising a fitting connecting the cooling airflow passage to the innerframe case and the bearing support member, wherein the fitting includesa transfer tube connecting the at least one spoke to a cup boss, thetransfer tube is fixed relative to the at least one spoke and moveablerelative to the cup boss.
 6. The mid-turbine frame of claim 5, furthercomprising a swirler tube connected to the fitting for directing coolingairflow in a direction of rotation of a low pressure rotor.
 7. Themid-turbine frame of claim 5, wherein the cooling airflow passageincludes a circular cross section in a first portion of the cup boss anda race track cross section in a second portion of the cup boss.
 8. Themid-turbine frame of claim 1, wherein the inner frame case and thebearing support member each include a race track shaped opening alignedwith the cooling airflow passage.
 9. A gas turbine engine comprising: amid-turbine frame located axially between a first turbine and a secondturbine, the mid-turbine frame comprising: an inner frame case; abearing support member located adjacent the inner frame case; and atleast one spoke attached to the inner frame case, wherein the at leastone spoke includes a cooling airflow passage extending through the innerframe case and the bearing support member.
 10. The gas turbine engine ofclaim 9, wherein the at least one spoke includes an elongatedcylindrical portion extending in a radial direction forming the coolingairflow passage having a branch extending in an axial direction.
 11. Thegas turbine engine of claim 10, wherein the cooling airflow passageincludes a branch extending in a radial direction.
 12. The gas turbineengine of claim 11, wherein the branch extending in the radial directionis in fluid communication with a bearing support cavity.
 13. The gasturbine engine of claim 9, further comprising a fitting connecting thecooling airflow passage to the inner frame case and the bearing supportmember, wherein the fitting includes a transfer tube connecting the atleast one spoke to a cup boss, the transfer tube is fixed relative tothe at least one spoke and moveable relative to the cup boss.
 14. Thegas turbine engine of claim 13, further comprising a swirler tubeconnected to the fitting for directing cooling airflow in a direction ofrotation of a low pressure rotor.
 15. The gas turbine engine of claim13, wherein the cooling airflow passage includes a circular crosssection in a first portion of the cup boss and a race track crosssection in a second portion of the cup boss.
 16. The gas turbine engineof claim 9, wherein the inner frame case and the bearing support membereach include a race track shaped opening aligned with the coolingairflow passage.